Vivaldi browser added support for MHTML, which is a web page archive format that saves the primary HTML page along with support files (ex. photos) into a single file.

This is a feature I had in Opera and have been waiting for it to show up in Vivaldi. I've seen the extensions of MHT and MHTML used for these files. Vivaldi saves them with an MHTML extension. Internet Explorer was able to recognize and open this in a test I just ran.